Semiautomatic screw-down control for rolling mills



s. H. RENDEL Y sEMIAUToMAgIc SCREW-Down CONTROL' Fbi: ROLLING MILLSocjf. 23, 1956 2 sheetslvsheet 2 Filed Aug: 6, 1952:-

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2,767,603 SEMIAUIOMATIC SCREW-DOWN CQNTRQL E93;

George H. Rendel, Pittsburgh, hPa., assignor ,to United vv,StatesStool.r Corporation, a corporation of- Nevv Jersey @pasatiempos s 1,952,senta .Noalla@ 11 Claims. (Cl. Vitl-556) Loto moolhiolr, nearer itstrailing ond thanelsovvhere, So Hnos by aS.- muoh as 8 to 10 poroout..Tfheserheavy ends, known as. mill run-downs, are tapered and normaillvY.begin to appear aPproXimalolv lQQ to 200` loer fjromthe trailing endpofeach strip.

The main factors whichcause mill run-downs, are believed t` o be' lossof tensionin the stripras' its trailing end leaves each roll stand andther lower temperature onthe strip hear its trailing end. It is`recognizd that substan- .tial savings would be realized byfeliminating `orminimizing` mill. run-downs.

"'Anobject. of 'the present invention is to provide an improved means.and method for reducinghot mill rundowns `by automatically turning downtheslrevlvs ona roll-"stand as the trailing end'of 'a' strip approaches"the stand and thereby compensating for the factorsv which Qa'userundowns; I i "A`fur`the'r object is to provide a semiautomatic controlfor screw `down nmotors, which control automatically 0pve'rates rst toturn d'own the' screws'as the trailing endyof approaches a roll standand `slibSequently,to reset-thescqr'evvs afterthe trailingend exits fromthis stand.

` Further objects/,are to provide lsuch-.a'control whichfhas irlaeslomaloallv Provolioe its ialorforavvifhi'oor- ,mlopi loo' of the.Sorow-oowo motors ,and vvhellorztiooallv Y havo a variable temperaturecompensating l. oeoomplshos .those and other` obiootsof-lllo ,iovontion, I have Provided improved ,detalls of str. oturo,

eared form of-wmchris shQwn' in no @con ons drawigsin which: Figaro lisaSohonoatlo Sido velevational View of .aooxios ofrolltStads ofy a hotStrip mill to whiohtho .Control of flolf osolioinvoaloo ,iS lapplied;Ijiglurezy is .al wiring diagram `ovfrtheyclontrol;` and Eigubre is awiringdiagrmof a modilication.

W .on tho ooolrolpof ,lhopr'osonl invention isfapplietlffo rollI standsother than'lthenfirst of a series,fva `on' ven'ent referencevpointffrorl,Which to operateth'e contr'olnls ljie exit ofnthe'trailing'end 'of eachstrip from a preceding stand. The control operates electrically, andI'hav'e illustrated a circuit which is set up by the entry ofeach striptothe roll stand two ahead of stand thus controlled and which isactuated by the exit of the strip from'this same standi However, itisapparent that equivalent 'results'can be obtained with other meanspreceding the controlled stand-for registering the passing-of the trail-,Patented Gets los ooo of .oooh Strip, for example a allolooloolrlo,coll oir-,a mechanically yactuated switch located' a properay'stipljerlg foiled.

Eigure l s'howsschematically three hnishinghst/andsll), 12 and 13 ofah'otQstrip mill. Each stand includes'worlc rolls 'Hand screws 1st-erregulating the separation bef Y A l l the `first stand 4l0 is 'thereference'stan'df'and the control isv applied to the A Stallo 134. aufil is apparent that Similafloonlrolo' oo' eioalodlo as many. otherv`Stands oIS dosirosl.

wooo flios rolls? la Elsloo The martyrs are energized frorrrD, C.1,1ine3s{i S 'p P passesthrough the roll standsfrorn. left thev circuitoordanoe. with, tho Present lnvonliolay to ,theldrive rnotor 1160i; .thereferencefrollstand 1,0cong lns a` load rolay- W. When motori-6 idlydrives the rolls, 1`4rofpstand Mbit d rayvs cornpara tivelyYsmallI currrent. lWhen a Astrip P actually is between thesey'rolls, the strip.resistsA theirl rotation; vconseqllellllly:- they IILOIrdrawsamuch-larger current' to, drivefthem; TheV relay yis adjustedtopiclcup (i. e. tobezactuated) whenrthe motor. draws,.thelargercurrentand itogdrop' out (\i. e. t'osbe deactuated) when themotor draws onlytheismalleridling current. Relay W has a setof'normally. opencontatifs W1,'(i. e. make-,andobreakmeans), and ashereinafter explained, operates the semiautomatic con-trolon'st'an'dl'lITh'escrewdown motors'll'A of the controlled rollstand 13 can'be operatedto raise or lower the kscrevvslS by the usual master controller, notshown, andare-:thus operated 'to move saidscrews to their initialYsetting. 'ti

accordancewith thepresent invention, the circuitfto these motorsincludes additional normally open contacts Di Whichwhen closed' completea circuit 'for operating the m'otors'to move the' screws down, and.addit'ionali'nrl mally opencontacts U1, which whenv closedc'or'ripleteia circuit for operating the motors to'`move"fthe"sere `A`up". These contacts' are inmdown aiidm'up relaysi'b Whe controlcircuit,- hereinafter described. `A magnetic-iclutfch 20 has its Vdriveelement oo nnected'to one` of lthelsicrews 15 of 'the rollstan'd 13'andits driven element connected to-acam 21 of a"gage-lirriity switchy 2 2in the-se control. As hereinafterexplained, n *Y is4 'engagedwhenlthes,reu/downirioto'rs are' e; rgihzed'via the 'contacts'DYror Uivo'f thesemiautomati'contro ,r otherwise is disengaged so that normaloneratiqmomqtors '17 `b`y their masterlkcontroller doesnotgil'llrferewith ooortioo offy fl'o '.Somlaotomatio oootolaodvoo al' 'Flavio 2,.shows 'details of oprolforrod cirooitffof. o @lill ytheSerniautornaticcontrol. VThe drive ,motor-of? e con` olled rollstand y13Ais .indicatiedat 21.3 andA load relayV lthereof at X. Thisload relayllikewisehasv af set of normally open contacts X1 (i. er make-,andybreakmeans); The controlA circuit isl energized? from A. lines .24;varrd 2,5and includes, downiand ,upfrelayslD and; Ur which contain theaforementioned; contacts. D1 'anrillrln` The controlcircuitincludeslsix;additionalre lays Y, Z, A, B, C, and S, a time delay:relayTDfaigage limitfsw'itch 22v already referred to, electronic vacuumtubes-26. and 27, potentiometers 28 and"29,fand astep down transformer30. Relay Y has,` one set'ofnornially open contacts Y1 and onesetyofnormally closedcoiitactstYr.V Relay Z has two sets. of.normally'opencontacts Z1 and Zz. Relay A has three sets of normally opencontacts A1, A2, and Aa. Relay B has six sets of nor mally open`contacts B1, Bs,k B3, B4, B5 and Bs. Relay C has two sets of normallyopen contacts C1 and C3 and one setof normally closed contacts C2. RelayS has one set of normally open contacts S1. Time delay relay TD has oneset of normally closed contacts TD1. Gage lirnitswitch 22 has one set ofnormally closed contacts 22a and one set of normally open contacts 22b.

` A pair of conductors 31 and 32 are connected to lines 24 and 25respectively. Conductor 32 contains a manual on-off"` switch 33 for thesemiautomatic control. Conductor 31 contains a set of normally closedcontacts 34, which lare in the master controller for the screw-downmotors 17." Whenever the operator uses the master controller to run thescrew-down motors in either direction, contacts 34 open andthusautomatically cut out the semiautomatic control. The coil of relay Yand the normally open contacts W1 of the load relay W of the referenceroll stand are connected in series across condu-ctors 31 and 3'2.Likewise the coil of relay Z and the normally open contacts X1 of theload relay Xof the controlled roll stand 13 are connected in seriesacross these same conductors. When the leading end of a strip P entersthe reference stand 10 and relay'W picks up, relay Y also picks up.`When the leading end of this strip enters the controlled stand 13 andrelay X picks up, relay Z alsofpicks up.` It follows that relays Y and Zalso drop t out when `the trailing end of the strip exits from therespective stands.

A `conductor 35, which contains the normally open contacts Y1, connectsone end of the coil of relay A with conductor 31. A conductor 36,` whichcontains the normally open contacts S1 andthe normally closed contactsTD1; connects the other end of this coil with conductor 32. Thus whenrelay Y picks up and its contacts Y1 close, they condition a currentpath through the coil of relay A from line 24 via conductors 31 and 3S,the relay coil, and conductors 36 and 32 to line 25. A conductor 37,which contains the normally open contacts Z1, connects one end of thecoil of relay S with conductor 31.

The other end of this coil is connected to conductor 32.`

Thus when relay Z 4picks up and its contacts Z1 close, relay `Salsopicks up. lClosing of contacts S1 completes the previously conditionedcurrent path through the coil of relay `A, and this relay also picks upand closes its contacts A1, A2 and Aa. Closing of contacts A1 seals inrelay A around contacts Y1, since contacts A1 are situated in a branchconductor 31a which is connected between .conductors 31 and 35 andshunts contacts Y1. Closing of contacts A3 seals in relay S aroundcontacts Z1, since contacts As are situated in a second branch conductor`31b which is connected between conductors 31a and.37 and shuntscontacts Z1.

A conductor` 38, which contains the normally open contacts A2, connectsconductor 32 with one end of the coil of` relay B. A conductor 39, whichcontains the normally closedcontacts Y2, connects the other end of thiscoil with conductor 31. Closing of contacts A2 conditions` a currentpath through this coil from Iline 24, via conductors 31 and 39, thecoil, and conductors 38 and 32` to line 25. At the stagewhere the stripis passing through lboth roll stands 10 and 13, relay Y is energized anditsnormally closed contacts Y2 are open, preventing 1 completion of thiscurrent path. summarizing, as long `as the strip P continues to passthroughboth roll stands 10 and 13,1relays W, X, Y, Z, A and S all areenergized, relays A and S being sealed in; relay B is conditioned,butinot `yet energized; relays C, D, and U` and time delay -relay TDhave not yet acted.`

Whenthe trailing end of the strip P exits from roll stand 10 and relaysW and Y drop out, contacts Y2 close and lcomplete the previouslyconditioned current path through the coil of relay B, which thereuponpicks up, and its `normally open contacts B1 to Bs all close. Closing ofcontacts B1 seals in relay B laround contacts Y2, since contacts B1 aresituated in a branch conductor 31e which =is connected betweenconductors 31 and 39 and shunts contacts Y2. A conductor 40, whichcontains the normally open contacts Z2 and B2, connects one end of thecoil of relay C with conductor 31. A conductor 41, which contains thenormally closed contacts 22a of the gage limit switch 22, connects theother end of this coil with conductor 32. Therefore closing of contactsB2 energizes relay C, its effect being later described. A con ductor 42,which contains the normally open contacts B3 connects conductor 31 withone `end of the timing element of the time delay relay TD. The other endof this element is connected to conductor 32. Therefore closing ofcontacts B3 completes the circuit to the time delay relay whichthereupon commences timing, its effect also being later described. Thedriving element of the magnet-ic clutch 20 is electrically connected toa current source 43, for simplicity illustrated as a battery, viaconductors 44 and 45 which contain the normally open contacts B4 and B5.Therefore closing these contacts engages the magnetic clutch andmechanically connects both the cam 21 and the slider of thepotentiometer 28 1 with one of the screws 1'5 of the roll stand 13.

The normally open contacts B6 are situated in conf ductor 32, which isconnected to one end of the coilsof both the down and up relays D and Ufor the screw-down motors 17 of the roll stand 13. The other ends of thecoils of relays D and U are connected to'I the plates of tubes 26 and 27respectively. The primary' winding of transformer 30 `is connected tolines 24 and 25; the secondary Winding of this transformer energizes thefilaments of both tubes via a pair of conductors 46 and.47. The cathodesof both tubes are connected to conductor 31 via conductort47, and aconductor 48 which is connected 'between conductor 47 and the branchconductor 31a. Thus closing of contacts Bs conditions a current paththrough the coils of both the down and up relays. For the down relaythis current path is -from line 24, `via conductors 31, 31a, 48 and 47,tube 26, the -relay coil, and conductor 32 to line 25. For the up relaythe current path is similar except that it is via tube 27. It is seenthat with the current paths thus set up, it is only necessary for one ofthe tubes 26 or 27 to become conductive for the relay D or U to pick up,close its contacts, and energize the screw-down motors 17.

For controlling the charge` on and 27, the circuit includes a Wheatstonebridge 50 which contains the aforementioned potentiometers 28 and` 29and is energized by a current source 51, for simplicity shown .as abattery. The slider of potentiometer 29 is adjustable manuallybeforehand to determine the distance the turn down screws are lowered bythe semiautomatic control. The slider of potentiometer 28 ismechanically -connected to the driven element of the mag netic clutch 20as already mentioned. The left ends of the resistors of bothpotentiometers are connected to the positive battery terminal, with avariable resistor R1 being interposed between potentiometer 28 and thebattery. The right ends of the resistors of both potentiometers areconnected to the negative battery terminals. A conductor 52 is connectedbetween the slider of potentiometer 28 and one contact each of thenormally open set C1, and the normally closed set C2. The other Contactof set C1 is connected to the slider of potentiometer 29 via a conductor53,1While the other contact o'f set C2 is connected to the negativebattery terminal via a conductor 54. Conductor 52 contains tworesistances Rz Vand R3.

The grids of tubes 26 and 27 are connected to conductor 52 viaresistances R4 and R5 respectively. In the t starting position shown inFigure 2, which is before relay C picks up, no current ilows throughconductor 52, 54 since both ends are at the same negative potentiaL Thegrids 0f both tubes have a negative charge so that neither the grids oftubes 26` .i-tsnow .closed contacts C3.

tribe.. eenduefins.- s.,.elreay expelled, relayl C Pieke 11' when een!,etea dese., wherjlutlllfit's. .imallyferil cts. .Cr and. Cfeleee andflsjnrmall'y eleeefd. e611- te'et ,C2 uien-v Cleeine ef in the relaystone-bridge, s'ince-.thefreis a di paniedby yclosingv ofcontacts'Ciunbalances,the Wheatsliderovf potentiometer 28. contact itsvresistor. Current now. flowsl from4 potentiometer. 29.through'conductor- 53, ,contactsv ,C1 and. conductorSZ-tolpotentiometer28. The effectifs tohapply ajpo'sitive chargetothe grid ofy tube 26.-Resistancuesv Re and Rapreven't'applic'ation of a similar ehajrgerb thegrid ,Qf tube 27. l

' 'Ifube 256. .becomesc0nducting,

contacts .the resistor thereot the and, .the current pathpreviously.conditioned. by. the ,closingnA ofn contacts. B3 vnow iscompleted. The ,down Dlrisv'energiz'ed and its .contacts D; close,completing currentfpath to. the yscrew.-dovvn motorsl to lowerfthescrews .llS of the controlled.grollfstand 13@ Rotation, of thescrews'rotates the cam the magnetic clutch beingengaged. WVCam 2n-1. operiatesthe gage limit switch, 22 andlopens 'its normally closed contacts 22aandV closes-its normally open contacts 22h. Opening of contactshelene-immediate effect, since. relay C is sealed in around-"them viaContacts 22h are situated .int a brarleh eenduefer 3.6.1.1r Whieh iSeeltleeted between eendueters $2 and 345i and. ehumeeentaete-TDL Aftereer-tee@ 212.1? eleee, the time delay-relay ED vtimes auf land itscontacts TD1 open, but relay-A remains-*energized via contacts-22hRotation .of the screws also moves the sliderl of potentiometer 28l tothe leftacross-the resistor thereof- -Utimetely it reeehes a peint whereits potential is the same as that of the slider of potentiometerwhereupon the -Wheatstone bridgeasainis inbelanee and current ceases toowthrough conductor 52, The

ceases- .to conduct current. .The down relay D drops. Out andl thescrew-down motors 1:7 stop. -It isy seen that the .grid y.of -.tubeY256y loses its posit-ive charge and the tube .distance whicht'nescrews.have been loweredbefore they stopis vdetermined byfthe position ofadjustment of pOen- .tiometer 29, since .this adiustment determines thepoint at which the .bridge vcomes into. balance..

:The screws lSzof the controlled stand 13, remainthus lowered until the.trailing end. ofthe strip exits fromthis .stand and. relays X` and Zdrop out. Contacts Zaopen as -.the latter relay drops out and. breaks.the current path to the coil of relay C, which also drops out.Theynormally. closed ycontacts. C2 .again .close` andV the normally.open .contacts C1 againy open. This action. agairnunvvbalances the-Wheatstone bridge Si?, with'the slider of the potentiometer 28 nowbeingmorepositive vthan the conductor' 54. -Current now flows frompotentiometer 28 through conductor 52, 54 in the opposite direction`f-rorn itsl previous ilow.` The grid of tube 27 attains a Apositivecharge and thetube becomes conducting. The 'previously conditionedcurrent path through the coil of `relay--U--has remained conditionedsince relay B still is energized. When tube -27 becomes conducting, thiscurrent Vpath is completed and relay U isA energizedVwherekupon itscontacts Ur close and complete the current path tofrnotors 17 forraising the screws. Resistances Re and Yiria 'prevent applicationof asimilar positive chargefto the grid'oftubef Rotation of the screwsagainrotates cam v21 and the slider of' potentiometer 28, sinceV themagnetic clutch 2t) remains'engaged, but rotates in the oppositedirection frombefloref The potentiometer slider again reaches itsfoi-ig'inalV .position at which the Wheatstone -bridge is in balance andcurrent flow ceases in conductor 52. .The

positive charge is removed from the `grid of tube 27,

.contacts 22b deenergizes relay la, whereupon its yThedistance which thescrews are Ijo'were'd is u' ldown lin `this' manner increases thepressure of the.`

whereupon this tubeA ceasesA toconduct current and re= :lay-'Udropsout.` i' The screw-'down'r'notors17'thsstp with the screws back at"their"originalsetting.l Aft-57th; same 'time cam 21 operates' gageflimit switch `22 returns ncontacts 22a'y to their normal'closedposition4 and :contacts 'tootheir normal Aopen position.lClosing'of contacts ,22a conditions the current path to rela' 'a thatylater'it can pickup for thenext 'strip4 Op contactsl A1, z and Agcpen.vQpening' ofj c ctsa'deenergizes relay B, while opening offcohtacts A3"de giges relay ,S. Opening of Icontacts Bswwhenrelayf dropsA outdeenergi'zes'the time delay relay: TD, andopenine-[Qi eenfeefe Brand B5deeneaees the manetieleluteh 20.' Thus the semiautomatic controlisfullyreset.

From the foregoing description it is .spleenfthat Vthe Serew-down meters17 Q11 the.eentr011ed"rellsfa @f1.3 automatically are operated to turndown the sere s I1x5 as the trailing end of each strip approach i by.thefposition of adjustment ofthe Slider .of 't tentiorneter 29, butonce the adjustmentis ma tliis distance is `the .same lfor all strips.Turning the news on theftrailing end portion of thestrip. P and thustends to reduethis portionto the. same thicknesses the remainder ,etthe` Strip.-

Figure 3 shows a modification. in the Wheats'tone to regulateautomatically the-distance which screws are turned down in accordancewith Variationslinth'e temperature ofthe strip.

It is, desirable that the vcooler the strip the farther the screws areturned down.

in Figure 3 two additional potentiometers 575- and .A516 are Connectedvin Series between the POSitl/e terminal# battery 51 and the resistor ofthe potentiometer 2:8.. The potentiometer 55 has a slider 57mechanically connected tof'a pyrometer indicator, not shown', but whichvis nresponsive tothe strip temperature. The pyrorneter moves the sliderin a direction to short out more andmore of the resistor of thepotentiometer the` vhotter the. strip. rIhe pyro'meter automaticallydisconnects itself from. the slider on attaining the. maximumtemperature `of the strip. The potentiometer 56 is manually operated andregulates the degree of compensation' fontmperatu're. The less of theresistor that is shunted. out` in. potentiometer 56, the more thetemperature compensation. It is seenthat the greater the resistancebetween the positive battery terminal and the vpotentiometer '28; thefarther the slider of this potentiometer must travel to balance thebridge. Consequently the colder the' strip, the greater the distancewhi'ch the' screws are' turned dpwnl An example using hypotheticalvalues may be helpfulrin understanding the temperaturecompensationfeaturel Assume thevoltage across the battery 51 `is 10Qvolts and the voltage drop across the potentiometers Y28, 55' and 56 isrespectively 50 volts,2 5 volts 'and 25 volts. "If thelfstrip beingrolled is to have the maximum of compensation for temperature, theslider ofthe potentiometerf56'i's ad justed sothat the potential fromthe slider is 50 volts positive when referred yto the negative batteryterminal; that is none of the resistor ofthis potentiometer isshunt'edout. To balance theVl/heatstonebridge,l the screw-down motors must lowerthe screws until tlieslrider'of potentionmeter 2,3 is at this samevoltage. If the l'strip is so cold that the slider 57 of potentiometer"55 does not move to short o ut any of the resistor of thispotentiometer, the voltage drop across potentiometer 23 remains 50Volts;the vscrewsarclowered by'an 'arrfont equal to the full travel ofthe slider of' potentiometer 2 8. Full travel on this potentiometermaybel equivalent'l to 0.100 inch vertical travel of the screwsjthereforewhen the strip is cold, the controls lower.the.screws0..l00.inch andlater return to their starting` position.

It the strip, is hot enough tomove. the slider 5]- etv potentiometer 55far enough `to short out allof the resistor, the voltage drop across thepotentiometer becomes zero. Now the voltage drops across potentiometers28 and 56 are .662/3 and 33% volts respectively. The screws are lowereduntil the slider of potentiometer 28 reaches a position that is 50 voltspositive. This position balances the bridge at a point where the slideris at 75 percent of full` travel, which corresponds with 0.075 inchvertical travel of the screwsp If the strip being rolled is to have theminimum of compensation for temperature, the slider of potentiometer 56is moved manually to shunt out all the resistance thereof. Now there isa voltage drop of 66% volts acros potentiometer 28 and 331/3 voltsacross potentiometer 55. For the` same setting on potentiometer 29 of 50volts from `its sliderto the negativeibattery terminal, when a cold.strip isirolled, the screw/down motors would lower the screws an,amount equivalent to 75 percent of4 full travel of the slider ofpotentiometer 28 to balance the bridge. When the strip is hot enough tomove the slider 57 of potentiometer 55` the full distance to shunt outall of its resistance, there would be 100 volts drop acrosspoitentiometer 28 and the slider of potentiometer 28 would move onlyhave its full travel to balance the bridge.

This example shows how the control can be regulated from `maximum tominimum temperature compensation by adjusting the slider ofpotentiometer 56.` The total amount which the screws are lowered can beregulated by adjusting the slider of potentiometer 29. Preferably bothpotentiometers 56 and 29 are located where they are convenient to themill operator.

' While two embodiments of my invention have been shown and described,it will be apparent that other adaptations and modifications may be madewithout departing from the scope ofthe following claims.

I claim:

l. In a hot strip rolling mill which includes a plurality of rollstands, each of which has. a pair of work rolls, a drive motorfor saidrolls, screws for regulating the separation between said rolls, andscrew-down motors for turning said screws up and down, one of saidstands being a reference stand anda succeeding stand beinga controlledstand, the combination with said controlled stand of a semiautomaticcontrol comprising load relays in the circuits of the drive motors ofsaid reference and said controlled stands, each of said relays beingadapted to pick up when a strip is between the rolls of its stand andotherwise to drop out, a control circuit connecting the load relay ofsaid reference stand and the screw-down motor of said controlled standfor turning down the screws of the latter stand whenthe load relay ofthe former stand drops out as the trailing end of a strip exitstherefrom, and means in said control circuit connected t0 the `loadrelay of said controlled stand for resetting the screws thereof whenthis relay drops out as the trailing end of the strip exits from saidcontrolled stand.

2. A combination as` defined in claim l in which said control circuitincludes a normally balanced Wheatstone i bridge, connections betweensaid bridge and the screwdown motor of said controlled stand foroperating this motor when said bridge becomes unbalanced, connectionsbetween said bridge and the load relay of said reference stand forunbalancing said bridge when this relay drops out as the trailing end ofa strip exits from this stand and thereby operating the screw-down motorof said controlled stand for turning down the screws thereof, and meansfor restoring the bridge to balance after the screws are turned down apredetermined distance.

3.` A combination as defined in claim 2 in which the re setting meansincludes connections between said bridge and the load relay of saidcontrolled stand for unbalancing said bridge when this relay drops outand means for restoring the bridge to balance when the screws return totheir original setting.

4. In a rolling mill for lengths of hot strip having leading andtrailing ends, which will include a series of tit) roll stands eachhaving a pair of work rolls, a drive motor for said rolls, screws forregulating the roll separation, and power means for turning said screwsup and down, said roll stands being adapted to roll a strip undertension and thus tending to leave a tapered thicker portion in the stripnear its trailing end, the remainder of the strip being of substantiallyuniform thickness, at least one of said stands being a controlled stand,the combination with said controlled stand of a control for the powermeans for its screws effective to turn them down as the portion of astrip near the trailing end is between the rolls of this stand and upafter the trailing end exits therefrom, but allowing the screws of thecontrolled stand to remain at settings attained independently of thecontrol when the rest of the strip is between the rolls thereof, saidcontrol comprising a circuit connected with the power means for thescrews of said controlled stand, a first make-and-break means in saidcircuit, means for actuating said first make-and-break means when theleading end of a strip passes a point lo cated a predetermined distanceahead of said controlled stand and for deactuating said firstmake-and-break means when the trailing end passes said point, a secondmakeand-break means in said circuit, means for actuating said secondmake-and-break means when the leading end passes said controlled standand for deactuating said second make-and-break means when the trailingend passes said controlled stand, means in said circuit conditioning acurrent path to the power means for the screws of said controlled standwhen both said make-and-break means are actuated, means in said circuitcompleting this current path to operate said last mentioned power meansto turn the screws down a predetermined distance when said firstmake-and-break means is deactuated, means for deenergizing said lastmentioned power means after the screws are turned down said lastmentioned predetermined distance, and means in said circuit completing acurrent path to operate said last mentioned power means to reset thescrews when said second make-and-break means is deactuated.

5. A combination as defined in claim 4 in which said firstmake-and-break means and the actuating and deactuating means thereforinclude a load relay in the circuit to the drive motor of a roll standpreceding said controlled stand, and said second make-and-break meansand the actuating and deactuating means therefor include a load relay inthe circuit to the drive motor of said controlled stand, said relayspicking up when a strip is between the rolls of the respective stands,but otherwise dropping out.

6. A comibnation as defined in claim 4 in which said circuit includesmeans for adjusting the predetermined distance by which the screws ofsaid controlled stand are turned down on completion of the current pathto the power means therefor.

7. A combination as defined in claim 4 in which said circuit contains abridge across which the power means for the screws of said controlledstand is connected, said bridge remaining in balance when the circuit isconditioned, and means for unbalancing said bridge when said rstmakeand-break means is deactuated to turn the screws down and again whensaid second make-and-break means is de actuated to turn the screws up.

8. A combination as defined in claim 4 in which said circuit includesmeans responsive to strip temperature for automatically varying thepredetermined distance by which the screws of said controlled stand areturned down in accordance with strip temperature.

9. In a rolling mill for lengths of hot strip having leading andtrailing ends, which mill includes a series of roll stands each having apair of work rolls, a drive motor for said rolls, screws for regulatingthe rolls separation and power means for turning said screws up anddown, said roll stands being adapted to roll a strip under tension andthus tending to leave a tapered thicker portion in the strip near itstrailing end, the remainder of the strip being of substantially uniformthickness, at least one of said stands being a controlled stand, thecombination with said con- 9 trolled stand of a control for the powermeans for its screws effective to turn them down as the portion of astrip near the trailing end is betwf,` :n the rolls of this stand and upafter the trailing end exits therefrom, but allowing the screws of thecontrolled stand to remain at settings attained independently of thecontrol when the rest of the strip is between the rolls thereof, saidcontrol comprising a bridge circuit having arms which contain normallybalanced adjustable resistances, electrical connections to the powermeans for the screws of said controlled stand connected across saidbridge circuit and thus normally keeping this power means deenergized, afirst make-and-break means connected to said bridge circuit, means foractuating said first make-and-break means when the leading end of astrip passes a point located a predetermined distance ahead of saidcontrolled stand and for deactuating said first make-and-break meanswhen the trailing end passes said point, a second make-and-break meansconnected to said bridge circuit, means for actuating said secondmakeand-break means when the leading end passes said controlled standand for deactuating said second make-andbreak means when the trailingend passes said controlled stand, successive actuation of both saidmake-and-break means conditioning said circuit and deactuation of saidrst make-and-break means unbalancing said circuit to energize the powermeans for the screws of said'controlled stand to turn them down apredetermined distance, and a mechanical connection between one of thelast mentioned screws and one of said adjustable resistances to restoresaid bridge circuit to balance and thus ydeenergize the power means whenthe screws are turned down said last mentioned predetermined distance,deactuation of said second make-and-break means unbalancing said bridgecircuit in the opposite direction to energize the power means for thescrews of controlled stand to reset these screws.

10. A combination as defined in claim 9 in which said mechanicalconnection includes a magnetic clutch normally disengaged to allowOperation of the power means for the screws of said controlled standindependently of said control, and said control comprises a circuit forengaging said clutch when the power means is operated by imbalance ofsaid bridge circuit.

11. A combination as dened in claim 9 in which said first make-and-breakmeans and the actuating and deactuating means therefor include a loadrelay in the circuit to the drive motor of a roll stand preceding saidcontrolled stand and said second make-and-break means and the actuatingand deactuating means therefor include a load relay in the circuit tothe drive motor of said controlled stand, said relays picking up when astrip is between the rolls of the respective stands but otherwisedropping out.

References Cited in the le of this patent UNITED STATES PATENTS1,814,354 Webster et al. July 14, 1930 1,969,536 Winne Aug. 7, 19342,003,160 Townsend May 28, 1935 2,275,509 Dahlstrom Mar. 10, 19422,300,990 Stoltz Nov. 3, 1942 2,339,359 Shayne Jan. 18, 1944 2,343,392Whitten Mar. 7, 1944

